1. Technical Field
The present invention relates to a numerical control apparatus for controlling a machine tool or the like.
2. Description of the Related Art
A numerical control apparatus (hereinafter referred to as "CNC apparatus") for controlling a machine tool or the like incorporates a programmable controller (hereinafter referred to as "PC") which performs sequence control. Such sequence control is performed by receiving auxiliary function signals (M function signal, T function signal) transmitted from a numerical control section and signals (cycle start signal, feed hold signal or the like) transmitted from the machine. Thereby control of the machine in cooperation with a processor of the numerical control section is performed.
On the other hand, there has recently been an increasing number of cases where a peripheral device, such as a loader used to load a work into a machine tool, a pallet changer or the like, is added to the machine tool as an option. In many of such cases, however, it is becoming necessary for the devices other than main machines such as machine tools to be sequence-controlled: Furthermore, such sequence controls need to be performed in cooperation with those for the CNC apparatus.
Conventionally, the following methods are adopted for performing sequence control on the peripheral device.
(1) executing the sequence control of the peripheral device also by a PC incorporated into the CNC apparatus.
(2) executing the sequence control of the peripheral device by a programmable controller connected to a separate external CNC apparatus.
The sequence program of the peripheral device has less independency and therefore must be interlocked with the operation of the CNC apparatus. For this reason, in order for the sequence program of the peripheral device to be executed by the PC incorporated into the CNC apparatus according the above method (1), it is necessary for the sequence program of the peripheral device to be incorporated into the sequence program specific to the PC in order to be connected therewith. Accordingly, the procedure for this incorporation becomes complex for a dealer or user, other than a designer of the sequence program of the CNC apparatus, in modifying or incorporating the sequence program of the peripheral device to be used as an option.
An attempt to alter an existing sequence program, by anyone who is not a designer of the sequence program specific to the CNC apparatus and not familiar with the sequence program, in order to incorporate thereinto the sequence program of the peripheral device, is likely to end up with errors because of his being unfamiliar with the programming procedure. Incorporation of an erroneous program leads to destruction of not only the sequence program of the peripheral device but also the primary sequence program, giving rise to an erroneous operation of the machine. This remarkably deteriorates the reliability of the system. Furthermore, in order to correct the mis-programming, it is necessary to correct also the primary sequence program, with the result that the correcting operation becomes very difficult to perform.
On the other hand, the above method (2) is free of the problems with the above method (1). However, it becomes necessary to provide what is otherwise unnecessary, such as a wiring for making connection between the PC incorporated into the CNC apparatus and an external programmable controller connected to the CNC apparatus, a main body of the external programmable controller, a power source for driving this main body, a locker for providing necessary space, and the like. Moreover, since development procedures of the editing function, diagnosis function, etc. (needed for developing the sequence program of the external programmable controller) differ, there arises the problem that the system development efficiency will decline.